TC 17S(FILIPO) to peak again within 24h//TC 18S to intensify steadily next 5 days//INVEST 94S//INVEST 93P//3 Week Tropical Cyclone Formation Probability//1315utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 18S. JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 17S.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 17S IS CURRENTLY TRACKING SOUTH-SOUTHWESTWARD ALONG THE WESTERN PERIPHERY OF A STR TO THE EAST. TC 17S IS FORECAST TO MAKE A SOUTHEASTWARD TURN WITHIN THE NEXT 6 HOURS AS THE STR PROPAGATES EASTWARD. THE SYSTEM WILL CONTINUE TRACKING ALONG WESTERN PERIPHERY OF THE STR AND INCREASE TRACK SPEED AS IT MAKES ITS WAY INTO THE BAROCLINIC ZONE AND INTERACTS WITH THE UPPER-LEVEL JET TO THE SOUTH. NEAR TAU 24, TC 17S IS FORECAST TO BEGIN SUBTROPICAL TRANSITION AND COMPLETE SUBTROPICAL TRANSITION BY TAU 36. AFTER A SUSTAINED SUBTROPICAL PERIOD (TAU 36 TO TAU 60) HAVING FEATURES OF BOTH TROPICAL AND EXTRATROPICAL SYSTEMS, THE SYSTEM IS FORECAST TO COMPLETE EXTRATROPICAL TRANSITION BY TAU 72. THE FORECASTED RISE TO PEAK INTENSITY OF 65 KTS AT TAU 24 IS PRIMARILY DUE TO THE INCREASED OUTFLOW ALOFT CAUSED BY THE TC POSITION RELATIVE TO THE UPPER-LEVEL MIDLATITUDE JET. FOLLOWING A PERIOD OF INTENSIFICATION TO TAU 24, VWS IS ANTICIPATED TO SHARPLY RISE AND INITIATE AN INTENSITY DOWNTREND.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN EXCEPTIONAL AGREEMENT WITH A MERE 50 NM CROSS-TRACK SPREAD AT TAU 48 AND A 90 NM CROSS-TRACK SPREAD AT TAU 72. AS SUCH, THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT WITH ALL GUIDANCE SUGGESTING AN INCREASE IN INTENSITY THROUGH TAU 24 WITH A WEAKENING TREND AFTERWARD. PEAK INTENSITY RANGES FROM 55 TO 75 KTS WITH COAMPS-TC (NAVGEM BASED) BEING AT THE HIGH END AND STATISTICAL-DYNAMICAL (GFS BASED) AT THE LOW END. THE JTWC INTENSITY PEAK IS PLACED SLIGHTLY HIGHER THAN CONSENSUS AT 65 KTS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED IMAGERY (EIR) DEPICTS TROPICAL CYCLONE (TC) 18S (EIGHTEEN) WITH A PARTIALLY EXPOSED AND INCREASINGLY DISORGANIZED LOW-LEVEL CIRCULATION CENTER. DUE TO HIGH EASTERLY SHEAR OVER THE SYSTEM, A WESTWARD TILTING VORTEX AND INTERMITTENT BURSTS OF CONVECTION INDICATE THE SYSTEM IS STRUGGLING TO TAP INTO GOOD OUTFLOW ALOFT. ENVIRONMENTAL ANALYSIS INDICATES THAT 18S IS IN A MARGINAL ENVIRONMENT FOR FURTHER INTENSIFICATION WITH WEAK TO MODERATE POLEWARD OUTFLOW ALOFT, HIGH (25-30 KTS) VERTICAL WIND SHEAR, OFFSET BY WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE BASED ON A 131200Z HIMAWARI-9 EIR IMAGE. THE INITIAL INTENSITY IS ALSO PLACED WITH LOW CONFIDENCE BASED ON THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18S IS CURRENTLY TRACKING SOUTHEASTWARD ALONG THE SOUTHERN PERIPHERY OF A NER TO THE NORTH. TC 18S IS FORECAST TO CONTINUE THIS TRACK UNTIL TAU 36, WHERE IT IS ANTICIPATED TO INITIATE A POLEWARD TURN IN RESPONSE TO A SUBTROPICAL RIDGE (STR) POSITIONED OVER WESTERN AUSTRALIA. THE SYSTEM IS FORECAST TO HAVE COMPLETED THE POLEWARD TURN NEAR TAU 72. AFTER TAU 72, TC 18S IS EXPECTED TO CONTINUE ON A SOUTHWESTWARD TRACK FOR THE REMAINDER OF THE FORECAST PERIOD. REGARDING THE INTENSITY FORECAST, TC 18S IS FORECAST TO MAINTAIN 35 KTS THROUGH TAU 12 DUE TO THE RELATIVELY DISORGANIZED STRUCTURE AND MARGINAL ENVIRONMENT. AFTER TAU 12, TC 18S IS FORECAST TO THEN GRADUALLY INCREASE INTENSITY THROUGHOUT THE DURATION OF THE FORECAST PERIOD AS THE SYSTEM TRACKS INTO A MARGINALLY FAVORABLE ENVIRONMENT WITH LESS VERTICAL WIND SHEAR VALUES (10-15 KTS) STARING AT TAU 36 AND SEA SURFACE TEMPERATURES REMAINING VERY WARM.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH A CROSS-TRACK SPREAD OF 325 NM AT TAU 72. GFS CONTINUES TO BE AN OUTLYING MODEL, TRACKING THE SYSTEM FURTHER EAST BEFORE STARTING THE POLEWARD TURN PREVIOUSLY DISCUSSED. THE JTWC TRACK FORECAST ALIGNS CLOSELY WITH ECMWF DETERMINISTIC AND ENSEMBLE MEMBER SOLUTIONS. MODEL GUIDANCE REMAINS FAIRLY DIVIDED REGARDING THE TIMING AND SHARPNESS OF THE POLEWARD TURN, AND AS SUCH, THE JTWC FORECAST TRACK IS PLACED WITH OVERALL LOW CONFIDENCE. INTENSITY GUIDANCE IS IN BETTER ALIGNMENT - RELATIVE TO TRACK AGREEMENT - WITH THE EXCEPTION OF COAMPS-TC. BY TAU 48, ALL JTWC INTENSITY CONSENSUS MEMBERS SUGGEST THAT TC 18S WILL INTENSIFY THROUGH TAU 120. THERE IS A 20 KT SPREAD IN THE INTENSITY GUIDANCE THAT PERSISTS FOR THE MAJORITY OF THE FORECAST INTERVAL, LENDING OVERALL MEDIUM CONFIDENCE IN THE JTWC INTENSITY FORECAST.

AN AREA OF CONVECTION (INVEST 94S) HAS PERSISTED NEAR 11.5S 129.3E, APPROXIMATELY 108 NM WEST-NORTHWEST OF DARWIN. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND A 130730Z HIMAWARI-9 VISIBLE SATELLITE IMAGE DEPICT A BROAD AREA OF TURNING WITH FLARING CONVECTION OBSCURING THE ASSESSED LLCC. ENVIRONMENTAL ANALYSIS INDICATES 94S IS IN A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH LOW TO MODERATE (10-15 KT) VWS, GOOD DUAL-CHANNEL DIVERGENCE ALOFT, AND WARM (29-31C) SEA SURFACE TEMPERATURES. GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 94S WILL CONTINUE TO TRACK GENERALLY EASTWARD OVER THE NEXT 24 HOURS, GRADUALLY CONSOLIDATING ALONG THE TRACK. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 23 TO 27 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.

GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 94S WILL CONTINUE TO TRACK GENERALLY EASTWARD OVER THE NEXT 24 HOURS, GRADUALLY CONSOLIDATING ALONG THE TRACK.

THE AREA OF CONVECTION (INVEST 93P) PREVIOUSLY LOCATED NEAR 11.4S 141.3E IS NOW LOCATED NEAR 11.4S 141.9E, APPROXIMATELY 76 NM NORTH OF WEIPA. ENHANCED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A BROAD WEAKLY DEFINED LLCC WITH FLARING CONVECTION OBSCURING THE LLCC. ENVIRONMENTAL ANALYSIS INDICATES 93P IS IN A FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH LOW TO MODERATE (15-20KTS) VERTICAL WIND SHEAR, WARM (29-30C) SEA SURFACE TEMPERATURES, COUPLED WITH ENHANCED EQUATORWARD OUTFLOW. GLOBAL MODELS ARE IN GOOD AGREEMENT THAT 93P WILL WEAKEN AS IT MOVES TOWARDS HIGH VWS (30-40KT). NUMERICAL MODELS HAVE 93P ADVANCING EAST-SOUTHEAST OVER THE NEXT 24 HOURS, BRIEFLY TRACKING OVER LAND, THEN FURTHER DECAYING AS IT MAINTAINS AN EAST-SOUTHEASTWARD TRACK. ENSEMBLES ARE IN DISAGREEMENT WHEN IT COMES TO INTENSITY WITH GEFS DISPLAYING MULTIPLE MEMBERS INTENSIFYING THE CIRCULATION WHEREAS ECENS MEMBERS ARE ON A SIMILAR TRACK BUT DO NOT REACH TC INTENSITY IN RECENT MODEL RUNS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 18 TO 22 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1005 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.

NUMERICAL MODELS HAVE 93P ADVANCING EAST-SOUTHEAST OVER THE NEXT 24 HOURS, BRIEFLY TRACKING OVER LAND, THEN FURTHER DECAYING AS IT MAINTAINS AN EAST-SOUTHEASTWARD TRACK. ENSEMBLES ARE IN DISAGREEMENT WHEN IT COMES TO INTENSITY WITH GEFS DISPLAYING MULTIPLE MEMBERS INTENSIFYING THE CIRCULATION WHEREAS ECENS MEMBERS ARE ON A SIMILAR TRACK BUT DO NOT REACH TC INTENSITY IN RECENT MODEL RUNS.

GTH Outlook Discussion Last Updated - 03/12/24 Valid - 03/20/24 - 04/02/24 The Madden-Julian Oscillation (MJO) remained robust during the past week, with the enhanced convective phase propagating from the Indian Ocean to the Maritime Continent. The RMM-based MJO index and CPC upper-level velocity potential based index both show strong amplitude, with clearly established eastward propagation at a phase speed consistent with canonical MJO activity. Widespread enhanced convection erupted over the eastern tropical Indian Ocean northwest of Australia, the strongest convection observed in that location for months, as the MJO destructively interfered with the low frequency El Nino base state. During the next two weeks, dynamical model MJO index forecasts show MJO activity propagating to the Pacific, with remarkable consistency among the various model systems and ensemble members depicting a strong, fast moving event. The forecast phase speed of the MJO as it propagates to the Pacific is more consistent with a convectively coupled Kelvin wave, and it is possible that constructive interference between the MJO, a Kelvin wave, and Rossby wave activity over the Pacific is helping to generate the strong projection of the index. Beyond Week-2, dynamical models still favor continued MJO activity across the Western Hemisphere, with spread among the ensemble members increasing. Based on these outlooks, the MJO is favored to play a substantial role in the evolution of the tropical convective pattern over the next several weeks. Constructive interference between the MJO and the decaying ENSO signal is favored for much of this outlook, which could lead to an enhancement of southern stream moisture across the southern tier of the CONUS. Although a trade wind disruption is likely to occur as the MJO crosses the Pacific, cooler water prevails across the upper layer of the Pacific basin, so any downwelling oceanic Kelvin wave activity will be shallow and short lived. If the MJO persists beyond Week-3, a trade wind surge across the Pacific could bring an end to El Nino conditions. Two tropical cyclones (TCs) formed during the past week. Tropical Storm Filipo formed over the Mozambique Channel on March 10, making landfall over Mozambique and then re-emerging over open water. Forecasts from the Joint Typhoon Warning Center (JTWC) show no additional threats to land from this system. Tropical Cyclone 18S formed on March 11 over the southeastern Indian Ocean, and is favored to gradually intensify. Impacts to Australia’s Kimberley Coast are possible within the next week. During the outlook period, strong MJO activity is tied to increased favorability for tropical cyclogenesis in the vicinity of Australia during Week-2, with potential formation areas shifting towards the Coral Sea as the MJO propagates eastward. Dynamical model forecasts show an increased chance for TC genesis over the Gulf of Carpentaria, warranting a 40 percent chance for formation during Week-2. During Week-3, the South Pacific is favored to become increasingly active, with the GEFS ensembles in particular depicting potential formations even east of the Date Line. Although the MJO can generate early season formations over the northwestern Pacific, dynamical model guidance is not supportive of development in that basin.